Japanese Unexamined Patent Publication No. 2000-312444 describes “including a first system for supplying first electric energy from one power source mounted on a vehicle to a first predetermined electric device for vehicle, a second system for supplying second electric energy from another power source mounted on the vehicle to a second predetermined electric device for vehicle, and a conversion/supply means which converts the second electric energy into the first electric energy to supply the converted energy to the first system” “to provide a power source supply device for vehicle capable of supplying desired electric power to each electric device for vehicle even though one power source is disordered”.
Furthermore, Japanese Unexamined Patent Publication No. 2000-312444 describes “including a remaining energy detection means which detects electric energy remaining amounts of the one power source and the other power source, and a power source selecting means which selects any one of the one power source and the conversion/supply means on the basis of the electric energy remaining amounts of the power sources to connect a selected one to the first system”.
Japanese Patent No. 4154883 describes “installing a drive control device including a communication circuit, a control circuit, and a drive circuit for driving a motor on a vehicle wheel side and supplying electric power to the drive control device from a vehicle body side through two power lines to drive a motor mounted on wheels so as to generate braking force” “to reduce the cost of power lines which electrically connect a vehicle body side to a vehicle wheel side to provide an inexpensive braking device”.
When a vehicle including a plurality of power sources illustrated in Japanese Unexamined Patent Publication No. 2000-312444 employs an electric braking device illustrated in Japanese Patent No. 4154883, the device requires power lines of two systems. Also when electric power depending on the maximum output of the device is supplied through the power lines, the power lines are required to be thick to some extent (large sectional areas) to minimize a voltage drop between both the ends of the power source lines. The thick power lines are hard to be bent. Vehicle wheels are relatively dislocated with respect to a vehicle through suspensions. Thus, the electric braking device is eagerly desired to have a configuration in which power lines for electrically connecting a vehicle body side to a vehicle wheel side are flexible.
The brochure of International Publication 2012/079969 discloses an electric braking device having a configuration in which “a rotational position of a spindle rotating by using drive torque of an electric motor when a friction member is pressed against a rotating member fixing to a wheel of a vehicle is turned back by a predetermined angle in an opposite direction of a side to which braking torque is applied by elastic force of a coil spring in failure”.
In the device described in the brochure of International Publication 2012/079969, in an initial stage in which braking torque is applied, energy must be accumulated in a coil spring first. More specifically, an output from an electric motor is used to wind up the coil spring. Thereafter, the output is used to increase the braking torque. For this reason, initial responsiveness (rising characteristics of braking torque) when the braking torque is increased is desired to be improved. In this configuration, since energy must be accumulated in the coil spring every braking operation, improvement is required also in terms of energy saving.